Sonic boom shaping - return of the SST

[DocM]

Aviation Week....

Shaped Boom Successes Increase Demand For Supersonic Demonstrator

Success in the wind tunnel is increasing pressure on NASA to find funds for a supersonic flight demonstrator to take low-boom testing out of the confines of Edwards AFB, Calif., and into communities not inured to sonic booms.

While confidence is growing that aircraft can be designed that have both low sonic boom and good cruise efficiency, exactly what level of boom the public will judge acceptable for routine supersonic flight over land is not so clear.

NASA is conducting flight research to validate its ability to reduce sonic booms, and to measure public response, but has to use Boeing F/A-18 supersonic fighters that fly a special maneuver to produce a shaped boom at a specific location. Meanwhile, the X-54 Low Boom Experimental Vehicle remains unfunded.

The F/A-18 was used in 2011 for the Superboom Caustic Analysis and Measurement Program (Scamp) to assess the focusing effect that occurs when a supersonic aircraft accelerates to cruise speed. As it goes from subsonic to supersonic speed, acoustic rays from the aircraft converge on a surface called a caustic, and the lens-like effect can produce a boom 5-10 times louder than in cruise.

Scamp is aimed at improving prediction codes and developing mitigation maneuvers. The 13 flights along the remote Black Mountain supersonic corridor north of Boron, Calif., generated 70 sonic booms, measured by a 2-mi. microphone array on the desert floor, a blimp tethered at 3,500 ft. and a quiet motor glider flying between the F/A-18 and the ground at 4,000-10,000 ft.

NASA also plans flights to validate its ability to predict over-the-top or secondary booms, caused by shockwaves that go up and away from the aircraft and travel long distances before reaching the ground. Compared with the traditional N-wave ?double-bang,? such booms are less predictable and have a more random, low-frequency rumbling signature.

F/A-18s were used for NASA's Waveforms and Sonic-boom Perception and Response (WSPR) project, completed in November. ?WSPR was a pilot study for future sonic boom community studies,? says Peter Coen, supersonics project manager. ?More than 100 volunteers provided subjective live responses to booms over a two-week period.? From Nov. 4-18, F/A-18s conducted 22 flights, generating 82 quiet and five normal booms. Precise times and boom intensities were recorded and participants used a phone app, web page or paper questionnaire to provide information every time they heard a boom while at home.

Earlier F-5E shaped-boom testbed vs. an unshaped-boom aircraft

Lockheed Martin concept

[neoadorable]

but can it do mach 4?

[DocM]

No, passenger supersonic flights will probably be limited to Mach 1.5 to 2.0 for noise reasons eve with the new techs, unless they go suborbital like Virgin Galactic wants to do with the SS2 follow-on. Then there is the Skylon which has already been wind tunnel tested to Mach 12 :)

[123456789A]

Can you make a sonic boom quiet to people on the ground by changing the direction of the boom?

[DocM]

Yes, direction and shape. That is what this research is all about. Recent experiments with a modified F-18 have brought the ground decibel level down from 120+db to only 83db, and the sound being a rumble rather than a sharp impulse. The target is to get it into the low 70's.

[neoadorable]

again with Skylon, that guy is becoming a pet peeve of mine :angry: mach 12 in a wind tunnel is great, but where is the real world application? how long will we need to wait? these are the same people that came up with tanks in a week and nuclear weapons in less than a decade, but a friggin suborbital plane takes them forever!